1. Field of the Invention
The present invention relates to a clamp of the type that rotates a clamp rod.
2. Explanation of Related Art
There is a conventional technique of the rotary clamp of this type which is constructed in the following manner, as disclosed in U.S. Pat. No. 5,820,118.
A clamp rod is inserted into a housing, an upper wall of which supports a halfway height portion of the clamp rod vertically movably. The clamp rod has a lower portion provided with a piston which is vertically movably supported by a barrel portion of the housing. The clamp rod is formed with a cam groove on an upper side of the piston. An engaging ball to be fitted into the cam groove is inserted into a recess provided in the barrel portion of the housing.
The conventional technique had a problem of being unable to smoothly rotate the clamp rod because a large frictional force acts from the engaging ball to the cam groove when rotating the clamp rod.
The present invention has an object to provide a clamp in which a clamp rod smoothly rotates.
In order to accomplish the above object, the present invention has constructed a rotary clamp in the following manner.
For example, as shown in FIGS. 1 to 4 or in FIGS. 7 to 10, a housing 3 supports a clamp rod 5 axially movably and rotatably around the axis. The clamp rod 5 is made movable for clamping from a first end wall 3a of the housing 3 to a second end wall 3b thereof. Within the housing 3, the clamp rod 5 has an outer periphery provided with guide grooves 26 peripherally in plural number. Each of the guide grooves 26 comprises a rotary groove 27 and a straight groove 28 which are provided in continuity with each other from the second end wall 3bto the first end wall 3a. Engaging balls 29 to be fitted into the respective guide grooves 26 are rotatably supported by through holes 31 provided in the housing 3. A sleeve 35 is externally fitted over the engaging balls 29 rotatably around the axis.
The above-mentioned invention offers the following advantage.
When the clamp rod rotates, for instance, in a clockwise direction when seen in plan, the engaging balls fitted into the rotary grooves of the clamp rod roll in a counter-clockwise direction when seen in plan. Simultaneously, the sleeve externally fitted over the engaging balls freely rotates in the counter-clockwise direction. This allows almost only rolling friction to act between an inner peripheral surface of the sleeve and every engaging ball, but hardly allows sliding friction to act therebetween. Therefore, a resistance which acts from the sleeve to every engaging ball is decreased. As a result, a frictional force which acts from every engaging ball to the rotary groove is reduced, thereby smoothly rotating the clamp rod with a light force.
The present invention includes the following rotary clamp.
For instance, as shown in FIGS. 1 to 4 or in FIGS. 7 to 10, the second end wall 3b of the housing 3 is constituted by a support cylinder 13. The clamp rod 5 is inserted into an inner wall 13a of the support cylinder 13. And the inner wall 13a is provided with the through holes 31. This invention has inserted the clamp rod into the inner wall of the support cylinder, which results in being able to form the inserted portion into a structure of a reduced diameter and decrease an inclination angle of the rotary groove. In consequence, it is possible to reduce the stroke required for rotating the clamp rod, thereby making the rotary clamp compact.
Further, the present invention includes the following rotary clamp.
For example, as shown in FIGS. 1 to 4, an annular piston 15 is inserted into the housing 3 axially movably. The clamp rod 5 is inserted into the piston 15. A radial bearing 24 is arranged between these piston 15 and clamp rod 5. This invention offers an advantage of being able to rotate the clamp rod more smoothly.
Moreover, the present invention includes the following rotary clamp.
For instance, as shown in FIGS. 1 to 4, the piston 15 faces an input portion 14 of the clamp rod 5 from a side of the first end wall 3a. There is provided between the piston 15 and the first end wall 3a, a first chamber 21 in which a clamp spring 20 is attached. And there is provided between the piston 15 and the second end wall 3b, a second chamber 22 to which pressurized fluid for unclamping is supplied. This invention offers the following advantage.
Upon unclamping, a force which has acted from the pressurized fluid in the second chamber to the piston is not applied to the clamp rod. This prevents an excessive force from acting on the rotary grooves and the engaging balls. Therefore, a rotary mechanism which comprises the rotary grooves and the engaging balls increases its service lifetime.
In addition, the present invention includes the following rotary clamp.
For example, as shown in FIGS. 7 to 10, the piston 15 faces an input portion 14 of the clamp rod 5 from a side of the first end wall 3a. There is provided between the piston 15 and the first end wall 3a, a first chamber 21 to which pressurized fluid for clamping is supplied. And there is also provided between the piston 15 and the second end wall 3b, a second chamber 22 to which pressurized fluid for unclamping is supplied. This invention offers the following advantage as well as the above-mentioned invention.
Upon unclamping, a force which has acted from the pressurized fluid in the second chamber to the piston is not applied to the clamp rod. This prevents an excessive force from acting on the rotary grooves and the engaging balls. Therefore, a rotary mechanism which comprises the rotary grooves and the engaging balls increases its service lifetime.